1. Field of the Invention
The present invention generally relates to a magnetic tape recording/reproducing apparatus, and particularly relates to a magnetic tape recording/reproducing apparatus that is used as an external storage device for a computer with use of a tape cassette, the magnetic tape recording/reproducing apparatus including a rotating drum and a tape loading mechanism and being capable of selectively loading a first tape cassette that accommodates a first magnetic tape having a first width W1 or a second tape cassette that accommodates a second magnetic tape having a second width W2 (e.g., twice the first width W1).
2. Description of the Related Art
Among streamer devices used as external storage devices for computers, those using tape cassettes and including rotating drums and tape loading mechanisms like video tape recorders have been commercialized.
Existing streamer devices have storage capacities as high as 72 GB in compression mode, for example. Yet, there is a market demand for streamer devices with larger storage capacities. In order to meet this demand, various manufacturers are developing new techniques for improving the streamer devices.
As one way of increasing the storage capacities of the streamer devices, a new tape cassette that accommodates a magnetic tape having a tape width greater than the tape widths of magnetic tapes accommodated in existing tape cassettes may be used.
Considering the fact that the existing streamer devices are still in use and that there are many existing tape cassettes in which information is recorded by the existing streamer devices, a new streamer device capable of using the new tape cassette needs to be compatible with the existing streamer devices, be capable of using the existing tape cassettes, and be capable of accurately reproducing information in the existing tape cassettes recorded by the existing streamer devices. The applicant of the present invention has developed a streamer device that meets the above demands. This streamer device is disclosed in Japanese Patent Laid-Open Publication No. 2006-107540.
This streamer device comprises a tape cassette loading mechanism, a rotating drum unit 200 (FIGS. 11A and 11B), and a tape loading mechanism. The tape cassette loading mechanism is configured to selectively load either a first tape cassette 10 that accommodates a first magnetic tape (hereinafter referred to as a 4 mm tape) 14 having a width W1 of 4 mm or a second tape cassette 20 that accommodates a second magnetic tape (hereinafter referred to as an 8 mm tape) 24 having a width W2 of 8 mm (see FIG. 2).
Referring to FIGS. 11A and 11B, the rotating drum unit 200 comprises a lower stationary drum 201 and an upper rotating drum 202. A lead 203 is provided on the peripheral surface of the stationary drum 201. The rotating drum 202 includes a rotating head (not shown). The rotating drum 202 rotates in the direction indicated by the arrow 205, i.e., in the counterclockwise direction when viewed from above. As shown exploded in FIG. 11C, the lead 203 has a simple spiral shape, extends about 180 degrees around the stationary drum 201 of the rotating drum unit 200, and has a lead angle of θ. The lead angle indicates the inclination angle of the lead 203 with respect to a rotation plane of the rotating head (a plane orthogonal to the center axis of the rotating drum unit 200).
If the 4 mm tape cassette 10 is loaded, the tape loading mechanism pulls out the 4 mm tape 14 from the 4 mm tape cassette 10 and, as shown in FIGS. 11A and 11B, winds the 4 mm tape 14 diagonally around the rotating drum unit 200 through an angle α1 (about 90 degrees) from a position S to a position E1 along the lead 203 so as to form a first tape path 210.
If the 8 mm tape cassette 20 is loaded, the tape loading mechanism pulls out the 8 mm tape 24 from the 8 mm tape cassette 20 and, as shown in FIGS. 12A and 12B, winds the 8 mm tape 24 diagonally around the rotating drum unit 200 through an angle α2 (about 180 degrees) from a position S to a position E2 along the lead 203 to form a second tape path 220. The position S from which the 4 mm tape 14 is wound onto the rotating drum unit 200 is the same as the position S from which the 8 mm tape 24 is wound onto the rotating drum unit 200.
In FIG. 13A, the 4 mm tape 14 wound on the rotating drum unit 200 and the 8 mm tape 24 wound on the rotating drum unit 200 are shown superposed. The 4 mm tape 14 and the 8 mm tape 24 are guided by the lead 203 by being in contact therewith at a lower edge 14a and a lower edge 24a, respectively. The lower edge 14a and the lower edge 24a are located in the same position.
When the 4 mm tape 14 runs on the peripheral surface of the rotating drum unit 200 in the direction indicated by the arrow 211, as shown in FIG. 13B, the rotating head scans the 4 mm tape 14 as indicated by the arrow 220 so as to form tracks 230 in tight contact with each other having inclination angles (hereinafter referred to also as track inclination angles) θ with respect to the longitudinal axis of the 4 mm tape 14, in which information is recorded. FIGS. 13B and 13C show the opposite sides of the magnetic film surfaces of the 4 mm tape 14 and the 8 mm tape 24. Strictly speaking, the inclination angles θ of the tracks 230 are different from the lead angle θ of the lead 203 due to running movement of the 4 mm tape 14. However, since the difference is very small, the track inclination angles θ of the tracks 230 are considered equal to the lead angle θ of the lead 203 for ease of explanation in this document.
When the 8 mm tape 24 runs on the peripheral surface of the rotating drum unit 200 in the direction indicated by the arrow 211, as shown in FIG. 13C, the rotating head scans the 8 mm tape 24 as indicated by the arrow 220 so as to form tracks 231 in tight contact with each other having inclination angles θ with respect to the longitudinal axis of the 8 mm tape 24, in which information is recorded.
It is to be noted that since the width of a recording track formed in a tape is made small for the purpose of increasing storage capacity, the allowable deviation of the trajectory of the rotating head from the recording track on the tape during reading operation is small.
<Patent Document 1> Japanese Patent Laid-Open Publication No. 2006-107540
The inventors of the present invention have found from a study on the behavior of the above-described streamer device that the state of contact of the lower edge 14a of the 4 mm tape 14 running on the peripheral surface of the rotating drum unit 200 in the direction indicated by the arrow 211 with the lead 203 is different from the state of contact of the lower edge 24a of the 8 mm tape 24 running on the peripheral surface of the rotating drum unit 200 in the direction indicated by the arrow 211.
Referring to FIG. 13A, a region 240 where the 4 mm tape 14 is in contact with the rotating drum 202 has an area of S4. A region 241 where the 8 mm tape 24 is in contact with the rotating drum 202 has an area of S8. The area S8 is not equal to the area S4. More specifically, the area S8 is greater than the area S4 (S8>S4).
In relation to the rotational direction of the rotating drum 202, both the 4 mm tape 14 and the 8 mm tape 24 are subjected to a force FZ1 that causes upward displacement of the 4 mm tape 14 and the 8 mm tape 24 at the starting side of winding on the rotating drum unit 200 due to contact with the rotating drum 202.
The upward displacement force FZ1 applied to the 8 mm tape 24 is greater than the upward displacement force FZ1 applied to the 4 mm tape 14 because of the relationship of S8>S4.
Accordingly, the 8 mm tape 24 wound on the rotating drum unit 200 is displaced upward at the starting side of winding on the rotating drum unit 200 as indicated by the one-dot chain line, which may result in forming a track 231a of a track inclination angle θ1 that is greater than the track inclination angle θ of the appropriate track 231 (θ1>θ).
Depending on the magnitude of the angle difference, the chance of errors occurring during reproduction of the 8 mm tape 24 that is properly recorded by other streamer devices may be increased.